1. Technical Field
The present invention contains subject matter related to Japanese Patent Application Nos. 2010-258650 filed in the Japanese Patent Office on Nov. 19, 2010 and 2010-258652 filed on Nov. 19, 2010, the entire contents of which are incorporated herein by reference.
The present invention relates to a connection structure and a connection method.
2. Related Art
In recent years, to reduce the space occupied as an installation place, printing apparatuses such as printers have been miniaturized while ensuring an inner space for reception of a sheet to be printed. The functions of a printing apparatus are controlled by a circuit board called a main board. However, there is also a demand for miniaturizing the main board as the printing apparatus is miniaturized.
To meet this demand, the main board does not provide all of the functions, but provides only main functions. A sub-board (daughter board) provides the functions of the printing apparatus, as in an operation panel operated by a user or a card reader such as a memory. This daughter board is efficiently disposed inside the printing apparatus. The daughter board and the main board are electrically connected to one another via a harness or a wiring member such as a ribbon cable or a flexible flat cable (FFC).
In general, power or an electric signal is transmitted through a transmission line formed by a pair of conductive lines. In an electronic apparatus, one of the pair of conductive lines is set to have a potential with the same level as a ground (GND) of a casing. At this time, since currents flow in opposite directions in one pair of conductive lines of the transmission line, magnetic fields formed by the conductive lines are cancelled by one another, and thus the magnetic field of the transmission line to the outside is not formed. Accordingly, there is no influence of noise radiated to the outside (hereinafter, this transmission type is referred to as a normal mode).
On the other hand, when currents flow in the same direction (same phase) in a pair of conductive lines, the currents are interpreted as returning to a noise source by stray capacitance of a space or the like (hereinafter, this transmission type is referred to as a common mode). When noise (common mode noise) in the common mode has a level in which the noise is returned to the noise source via the space stray capacitance or the like, the amount of current is very small. Therefore, there is generally no problem of EMC (Electromagnetic Compatibility). However, when coupling with a space occurs by resonance or the like, the energy of the noise flows out to the space, and thus the noise current increases. As a result, a problem with EMC occurs since the noise may not be suppressed to a level equal to or less than a regulated noise radiation level.
For example, when the main board and the daughter board are connected by a wiring member, a common mode is formed in a signal line and a GND line due to mismatch or the like between transmission impedance and signal impedance of wiring patterns or wiring members to be used in connector sections of the boards. Further, in the wiring member, the common mode noise flows in a power line in addition to the signal line and the GND line via a bypass capacitor between the GND and a power source. In some cases, noise with the same phase may be superimposed one another in many lines of the wiring member including the signal line, the power line, and the GND line.
Further, when the length of the wiring member approximates a quarter or half of the equivalent wavelength of the superimposed noise, the noise (high-frequency) current resonates in the length direction of the wiring member and couples with a space, and thus the noise is radiated to the outside. At this time, since the high-frequency current radiated sequentially from the noise source is supplied with the same phase to each line of the wiring member, noise with a level exceeding the regulation value of noise regulation of an apparatus is radiated.
A countermeasure of the common mode noise is necessary, but it is difficult for an LCR circuit that includes a resistor, a coil, and a capacitor to implement a countermeasure since the noise with the same phase is superimposed in the power line, the signal line, or the GND line. Therefore, when the common mode noise is superimposed in the wiring member, the wiring member is tightly pressed on a casing ground, as disclosed in JP-A-2007-311709, or a common mode choke or a ferrite core is inserted, as disclosed in JP-A-2006-191006, to prevent the transmission of the common mode noise or suppress radiation of the common mode noise toward a space.
However, this structure is configured on the assumption that the casing ground is provided in the vicinity of the wiring member, and thus this structure may cause large restriction on the degree of freedom of product design. Further, the volume of the ferrite core is necessarily large to obtain a sufficient effect of the countermeasure of the ferrite core or the like and a member that fixes the ferrite core is necessarily prepared and provided inside the product casing. Furthermore, since it is necessary to perform a work of winding the wiring member around the ferrite core, considerable difficulty and cost are caused in the assembling process.